Meaning
Metal deformation defects occur when excessive clamping forces press mold halves together and crush the parting line faces. Tooling engineers watch for parting line hobbing in multi-cavity injection molds when high clamp tonnages concentrate force on small shutoff areas. This crushing damages the tool steel and creates gaps that allow molten plastic to flash.
Defect Mechanism
Excess force exceeds the yield strength of the steel, causing plastic deformation. The parting line hobbing defect arises when incorrect clamping pressures concentrate loads. Once deformed, the tool can no longer seal.
Tooling Prevention
Mold designers calculate shutoff surface areas and limit clamp force to prevent the compressive stress from exceeding material limits. Mitigating parting line hobbing requires utilizing harder tool steels or incorporating safety lands that distribute the clamping force evenly. Regular mold maintenance and pressure calibration are necessary to ensure that load distributions remain uniform during production.
Repair Method
Restoring deformed parting lines requires machining away the damaged steel and rebuilding the face using precision welding. After addressing parting line hobbing, the toolroom must re-machine and hand-bench the shutoff surfaces to ensure a perfect match. This repair is time-consuming and expensive, which is why molders focus on preventing the issue by using torque limits and regular tonnage calibrations during press setups.
